Method for decoding a stream of coded data representative of a sequence of images and method for coding a sequence of images

Abstract

A method for decoding a stream of coded data representative of a sequence of images is disclosed. The decoding method comprisesdetermining a prediction block,calculating the average of said prediction block,reconstructing, from said stream, a DC coefficient and AC coefficients relating to said current block,calculating an average of said current block from said average of said prediction block and said DC coefficient,calculating a weighted prediction parameter as being the ratio of the average of said current block and the average of said prediction block,transforming a block of coefficients comprising a null value as DC coefficient and said reconstructed AC coefficients into a residual block,reconstructing the current block by merging said residual block and said prediction block weighted by said weighted prediction parameter.A method for coding is further disclosed.

Description

SCOPE OF THE INVENTION[0001]The invention relates to the general domain of image coding. More specifically, the invention relates to a method for decoding a stream of coded data representative of a sequence of images and a method for coding a sequence of images.PRIOR ART[0002]The majority of methods for coding a sequence of images into a stream of coded data and methods for decoding this stream use temporal prediction or inter-image prediction and equally spatial prediction or intra-image prediction. Intra-image prediction or inter-image prediction enables the compression of an image sequence to be improved. It comprises, for a current block, the generation of a prediction block and the coding of a difference, also called a residual block, between the current block and the prediction block. The more the prediction block is correlated with the current block, the lower is the number of bits required to code the current block and therefore the more effective is the compression. However...

AI Technical Summary

Benefits of technology

[0071]The coding and decoding methods according to the invention have the advantage of improving the prediction method by taking account of the content of the current block, i.e. notably by not being limited to the content of its neighbourhood, and of adapting dynamically to the local variations of illumination without having to explicitly code the parameters relating to these local variations They also have the advantage of improving the coding efficiency in the case where no weighted prediction parameter is transferred in the stream.

Problems solved by technology

However, inter-image (respectively intra-image) prediction loses its efficiency when there is a luminosity variation between the images of the sequence (respectively in the current image).

However, such a method is costly in terms of bitrate as it implies the transmission in the stream of a set of weighted prediction parameters per image slice and thus potentially per block.

However, such a prediction method is less precise than the preceding method in that the weighted prediction parameter(s) associated with the current block Bc do not take into account the content of the block.

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